The proposed work consists of studies of enzyme and tissue metabolism in iron deficient rats and rat embryo-fetuses and human white blood cells to determine the nature of the enzymatic abnormalities which may be produced and the resultant metabolic changes. Particular emphasis will be placed on studies of brain, brown fat, and muscle tissues and white blood cells in order to determine the molecular basis for abnormalities in behavior, muscular weakness, immunologic changes, and cold adaption which have been described in iron deficient animal and human subjects. In other studies, it is planned to examine at the biochemical level the proposed defective conversion of thyroxin (T4) to triiodothyronine (T3) in iron deficiency and to determine the mechanism by which this occurs by purifying and studying the specific iodinase which is responsible for the enzymatic reaction.